1. Field of the Invention
The present invention relates to a fixing apparatus applicable to an image forming apparatus such as a copying machine or a printer, and more particularly to an apparatus for coating a fixing member with a releasing agent.
2. Related Background Art
As an example of such image forming apparatus, there is conventionally known an apparatus equipped with a fixing apparatus 150 as shown in FIG. 12.
As detailedly shown in FIG. 12, the fixing apparatus 150 is provided with a fixing roller 151 constituting a rotatably provided fixing member, a pressure roller 152 constituting another fixing member (pressurizing member) rotated in pressurized contact with the fixing roller 151, a releasing agent applying (coating) apparatus 153, and roller cleaning apparatuses 154, 155. The fixing roller 151 and the pressure roller 152 are respectively provided therein with heaters 156, 157 constituting heating means an composed for example of halogen lamps. Thermistors 158, 159 are so positioned as to be respectively in contact with the fixing roller 151 and the pressure roller 152 and control the voltages supplied to the heaters 156, 157 through temperature adjusting circuits thereby executing adjustment of the surface temperature of the fixing roller 151 and the pressure roller 152.
On the fixing roller 151 there are mounted the cleaning apparatus 154 and the releasing agent coating apparatus 153. The cleaning apparatus 154 cleans the fixing roller 151 by removing the toner etc. deposited thereon by offsetting, and the releasing agent coating apparatus 153 coats a releasing agent such as silicone oil onto the fixing roller 151 thereby facilitating the separation of a transfer paper P, constituting the recording material, from the fixing roller 151 and prevents the toner deposition by offsetting.
The cleaning apparatus 154 is composed of a cleaning web 154a consisting of a heat-resistant web-shaped non-woven cloth, a pressure roller 154b for pressing the cleaning web 154a to the fixing roller 151, an unwinding roller 154c for feeding the new cleaning web 154a, and a winding roller 154d for gradually winding the cleaning web 154a which is deteriorated in the cleaning ability for example by deposition of toner. The cleaning apparatus 154 is provided upstream of the thermistor 158 in the rotating direction of the fixing roller 151, in order to protect the thermistor 158 from detection error resulting from the sticking thereto of the offset toner.
When a predetermined number of copying operations is judged by a counter, a solenoid (not shown) is energized to activate a one-way clutch to wind the cleaning web 154a by a predetermined amount, in a direction opposite to the rotating direction of the roller. Such winding in the opposite direction avoids dragging of the cleaning web 154a in the rotating direction of the roller.
The releasing agent coating apparatus 153 is composed of an oil tank 153a or a releasing agent container for containing the releasing agent such as silicone oil, and a coating roller 153d constituting releasing agent supply means which bears the releasing agent on oil, picked up by pickup rollers 153b, 153c from the oil tank 153a, for supply onto the surface of the fixing roller 151, and a regulating blade 153e consisting of an elastic member is so provided as to abut on the coating roller 153d for maintaining a constant oil amount thereon, thereby attaining uniform oil coating onto the fixing roller 151. The releasing agent coating apparatus 153 is positioned downstream of the thermistor 158 in the rotating direction of the fixing roller 151.
Also the pressure roller 152 is provided with a cleaning apparatus 155 composed, similarly to the cleaning apparatus 154, of a cleaning web 155a, a pressure roller 155b, an unwinding roller 155c and a winding roller 155d, in order to remove the toner on the pressure roller 152 transferred from the fixing roller 151.
On the pressure roller 152, there abuts an oil removing blade 160 consisting of an elastic member for removing the excessive releasing agent remaining on the pressure roller 152. Without such oil removing blade 160, the excessive releasing agent is accumulated in the nip of the fixing roller 151 and the pressure roller 152, eventually causing a stain on the recording material or failure in the entry into the nip in certain recording material such as a transparent laminate OHP film. The oil removing blade 160 is composed for example of silicone rubber or fluorinated rubber, and abuts on the pressure roller 152 with an appropriate amount of intrusion in the opposite (or forward) direction with respect to the rotating direction of the pressure roller 152.
When a transfer paper P is conveyed in such configuration, the fixing roller 151 and the pressure roller 152 are rotated and silicone oil as the releasing agent is coated on the surface of the fixing roller 151. Thus, while passing between the fixing roller 151 and the pressure roller 152, the transfer paper P is pressed and heated by substantially constant pressure and temperature from both surfaces, whereby the unfixed toner image on the paper is fused and fixed to form a full-color image thereon. The transfer paper P bearing the fixed image is separated by an under separation claw 168 from the pressure roller 152 and is discharged from the apparatus.
However, such conventional image forming apparatus has been associated with the following drawbacks.
Firstly, the heat fixing apparatus in the ordinary copying machine waits for a predetermined period, after the power supply is turned on, until the fixing roller reaches a predetermined temperature, and the copying operation is enabled after such predetermined temperature is reached. However the fixing ability is different between immediately after the copying operation is enabled (xe2x80x9cfirst run in the morningxe2x80x9d) and after the lapse of a certain time in the copy-enabled stand-by state (xe2x80x9cstanding statexe2x80x9d). Such phenomenon arises from the difference, between the first run in the morning and the standing state, not only in the surface temperature of the fixing roller but also the temperature of the entire fixing apparatus and that of the releasing agent to be coated on the surface of the fixing roller.
More specifically, in the standing state, the heat of the fixing roller is transferred to the releasing agent through the coating roller and the pickup rollers thereby elevating the temperature of the releasing agent. In such state, the temperature loss of the fixing roller is limited when the releasing agent is coated thereon, and the releasing agent present between the fixing roller and the toner is also heated, whereby satisfactory fixing ability is secured. On the other hand, in the first run in the morning, the releasing agent is still cold and the fixing roller shows an abrupt temperature loss when such releasing agent is coated thereon, and the releasing agent of a low temperature is present between the fixing roller and the toner, whereby the fixing ability is deteriorated. Such phenomenon becomes more conspicuous in an environment of low temperature.
In order to avoid such drawback, the present applicant already proposed a fixing apparatus, provided, as shown in FIG. 13, with a releasing agent heating member 180 composed of a heat generating member or a heater 182, a heat conductive member 181 composed for example of a metal, a temperature of the heater 182, a safety element 184 for preventing excessive temperature of the heater 182 etc., setting to heat the releasing agent in the oil tank 153a. 
In such fixing apparatus, the temperature detecting element 183 detects the temperature of the heater 182, and, if the detected temperature is lower than a desired temperature, the heater 182 of the releasing agent heating member 180 is powered to elevate the temperature of the heater 182. The heat of the heater 182 is transmitted through the heat conducting member 181 to elevate the temperature of the releasing agent. When the heater 182 reaches the desired temperature, the electric power supply thereto is cut off whereby the temperature of the releasing agent is no longer elevated.
In such configuration, however, the releasing agent may not reach an appropriate temperature, since the power supply to the heater 182 is controlled by the temperature detecting element 183 for detecting the temperature of the heater 182.
An object of the present invention is to provide a fixing apparatus capable of heating the releasing agent to an appropriate temperature.
Another object of the present invention is to provide a fixing apparatus capable of preventing excessive heating of the releasing agent, thereby achieving satisfactory fixation.
Still another object of the present invention is to provide a fixing apparatus comprising a fixing member for fixing an unfixed image onto a recording material, a containing portion for containing a releasing agent, applying means for applying the releasing agent in the containing portion on the fixing member, heating means for heating the releasing agent in the containing portion, and detection means for detecting a temperature of the releasing agent in the containing portion, wherein heating of the heating means is controlled based on a detected temperature from the detection means.
Still another object of the present invention is to provide a fixing apparatus comprising a fixing member for fixing an unfixed image onto a recording material, a containing portion for containing a releasing agent, applying means for applying the releasing agent in the containing portion on the fixing member, heating means for heating the releasing agent in the containing portion, first detection means for detecting a temperature of the releasing agent in the containing portion, and second detection means for detecting a temperature of the temperature of the heating means, wherein heating of the heating means is controlled based on detected temperature from the first detection means and the second detection means.
Still other objects of the present invention, and the features thereof, will become fully apparent from the following description.